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<p>在web开发啊过程之中遇到了这么一个文件，想用浏览器下载一个mp4文件，当初思想简单，没想那么深，直接把MP4文件放在了静态资源文件夹中，直接启动服务器，将url指向了该文件，然后浏览器没能如我所愿，去下载这个文件，而是在浏览器中打开了该文件。我也是很无奈，看来事情没那么简单，多方打听，终于明白了这个原理。</p>
<p>原来服务端向客户端游览器发送文件时，如果是浏览器支持的文件类型，一般会默认使用浏览器打开，比如mp4、txt、jpg等，会直接在浏览器中显示，而不是下载该文件。</p>
</blockquote>
<h2 id="如何处理"><a href="#如何处理" class="headerlink" title="如何处理"></a>如何处理</h2><blockquote>
<p>如果想要下载文件而不是打开文件，则需要在服务器端的响应头加上相应的头部信息。</p>
</blockquote>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 首部字段ContentType说明了实体主体内对象的媒体类型，这是一个二进制文件类型</span></span><br><span class="line"><span class="string">'Content-Type'</span>: <span class="string">'application/octet-stream'</span></span><br><span class="line"></span><br><span class="line"><span class="comment">//  Content-Disposition 消息头指示回复的内容该以何种形式展示，是以内联的形式（即网页或者页面的一部分），还是以附件的形式下载并保存到本地。</span></span><br><span class="line"><span class="string">'Content-Disposition'</span>: <span class="string">'attachment; filename=1.mp4'</span></span><br><span class="line"></span><br><span class="line"><span class="string">'Content-Length'</span>: <span class="number">1024</span></span><br></pre></td></tr></table></figure>
<h3 id="Content-Type"><a href="#Content-Type" class="headerlink" title="Content-Type"></a>Content-Type</h3><blockquote>
<p>Content-Type 实体头部用于指示资源的MIME类型 media type 。</p>
<p>在响应中，Content-Type标头告诉客户端实际返回的内容的内容类型。</p>
</blockquote>
<h3 id="Content-DisPosition"><a href="#Content-DisPosition" class="headerlink" title="Content-DisPosition"></a>Content-DisPosition</h3><blockquote>
<p>在HTTP场景中，第一个参数或者是inline（默认值，表示回复中的消息体会以页面的一部分或者整个页面的形式展示），或者是attachment（意味着消息体应该被下载到本地；大多数浏览器会呈现一个“保存为”的对话框，将filename的值预填为下载后的文件名，假如它存在的话）。</p>
</blockquote>
<h2 id="nodejs-express-实例"><a href="#nodejs-express-实例" class="headerlink" title="nodejs express 实例"></a>nodejs express 实例</h2><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> express = <span class="built_in">require</span>(<span class="string">'express'</span>);</span><br><span class="line"><span class="keyword">var</span> router = express.Router();</span><br><span class="line"><span class="keyword">const</span> fs = <span class="built_in">require</span>(<span class="string">"fs"</span>);</span><br><span class="line"><span class="keyword">const</span> path = <span class="built_in">require</span>(<span class="string">"path"</span>);</span><br><span class="line"><span class="keyword">const</span> PUBLIC_PATH = path.resolve(__dirname, <span class="string">'../public'</span>);</span><br><span class="line"></span><br><span class="line"><span class="comment">/* GET home page. */</span></span><br><span class="line">router.get(<span class="string">'/'</span>, <span class="function"><span class="keyword">function</span>(<span class="params">req, res, next</span>) </span>&#123;</span><br><span class="line">  res.render(<span class="string">'index'</span>, &#123; <span class="attr">title</span>: <span class="string">'Express'</span> &#125;);</span><br><span class="line">&#125;);</span><br><span class="line"></span><br><span class="line">router.get(<span class="string">'/download/:path'</span>, <span class="function"><span class="keyword">function</span>(<span class="params">req, res, next</span>) </span>&#123;</span><br><span class="line">  <span class="comment">// 获取参数</span></span><br><span class="line">  <span class="keyword">let</span> filePath = req.params.path;</span><br><span class="line">  <span class="comment">// 拼接文件的绝对路径</span></span><br><span class="line">  <span class="keyword">let</span> downloadPath = path.resolve(PUBLIC_PATH, filePath);</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 得到文件名</span></span><br><span class="line">  <span class="keyword">let</span> &#123;<span class="attr">base</span>: fileName&#125; = path.parse(downloadPath);</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 文件的信息</span></span><br><span class="line">  <span class="keyword">let</span> stat;</span><br><span class="line">  <span class="keyword">try</span>&#123;</span><br><span class="line">    <span class="comment">// 通过fs模块获取文件的信息，报错就代表着不存在该文件</span></span><br><span class="line">    stat = fs.statSync(downloadPath);</span><br><span class="line">  &#125;<span class="keyword">catch</span>(error) &#123;</span><br><span class="line">    <span class="comment">// 不存在该文件</span></span><br><span class="line">    <span class="keyword">return</span> res.status(<span class="number">404</span>).end();</span><br><span class="line">  &#125;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 获取文件的大小</span></span><br><span class="line">  <span class="keyword">let</span> &#123;<span class="attr">size</span>: total&#125; = stat;</span><br><span class="line">  <span class="comment">// 设置响应头信息，指示内容应该被下载</span></span><br><span class="line">  res.setHeader(<span class="string">"Content-Disposition"</span>, <span class="string">"attachment; filename="</span>+fileName);</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 说明了实体主体内对象的媒体类型，这是一个二进制文件类型</span></span><br><span class="line">  res.setHeader(<span class="string">"Content-Type"</span>, <span class="string">"application/octet-stream"</span>);</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 响应状态为200</span></span><br><span class="line">  res.status(<span class="number">200</span>);</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 通过fs模块创建二进制流，并将其二进制流推送到响应主体中</span></span><br><span class="line">  fs.createReadStream(downloadPath).pipe(res);</span><br><span class="line">&#125;);</span><br><span class="line"></span><br><span class="line"><span class="built_in">module</span>.exports = router;</span><br></pre></td></tr></table></figure>
<h2 id="下载文件为中文文件名时"><a href="#下载文件为中文文件名时" class="headerlink" title="下载文件为中文文件名时"></a>下载文件为中文文件名时</h2><blockquote>
<p>探究 Content-Disposition：解决下载中文文件名乱码</p>
<p>直接在Content-Disposition中设置中文会导致乱码。</p>
<p>首先要注意的是disposition-type。由上面给出的是Content-Disposition header 字段我们可以知道，Content-Disposition有两种type，即inline和attachment。根据文档中的介绍可知，inline类型会自动显示附件内容，比如显示一个图片；而attachment不会自动显示，在邮件中可能会显示为一个带图标的附件，在浏览器中可能会提示下载。</p>
<p>其次就是disposition-parm。主要作用就是提供一个建议的文件名（filename-parm），客户端（浏览器、邮件系统）在尽可能的情况下会以该文件名去保存文件。尽可能的意思是存在不一样的情况，比如文件名非法、存在同名文件，这些情况下客户端会采取一些措施，比如修改文件名。</p>
<p>最后看看filename-parm的value。这个value就是文件名（本文的目的是给value设置一个中文，主要的坑就是这里）。</p>
<p>通过上面的介绍，要给前端发送一个文件，并且定义文件的名字为中文，可以在发送文件之前返回这样一个HTTP Response Header ：</p>
</blockquote>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">Content-Disposition: attachment; filename=文件.txt</span><br></pre></td></tr></table></figure>
<p>但是，如果你这样做了，服务器就会报错。</p>
<blockquote>
<p>原因：需要注意的是，RFC 822（ Standard for ARPA Internet Text Messages）规定了文本消息只能为ASCII，因此这个Content-Disposition是非法的。</p>
<p>在nodejs中，需要将中文文件名给处理一下，如下代码</p>
</blockquote>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 设置响应头信息，指示内容应该被下载</span></span><br><span class="line">  res.setHeader(<span class="string">"Content-Disposition"</span>, <span class="string">"attachment; filename="</span>+ <span class="built_in">encodeURIComponent</span>(fileName));</span><br></pre></td></tr></table></figure>
<p>完整代码：</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> express = <span class="built_in">require</span>(<span class="string">'express'</span>);</span><br><span class="line"><span class="keyword">var</span> router = express.Router();</span><br><span class="line"><span class="keyword">const</span> fs = <span class="built_in">require</span>(<span class="string">"fs"</span>);</span><br><span class="line"><span class="keyword">const</span> path = <span class="built_in">require</span>(<span class="string">"path"</span>);</span><br><span class="line"><span class="keyword">const</span> PUBLIC_PATH = path.resolve(__dirname, <span class="string">'../public'</span>);</span><br><span class="line"></span><br><span class="line"><span class="comment">/* GET home page. */</span></span><br><span class="line">router.get(<span class="string">'/'</span>, <span class="function"><span class="keyword">function</span>(<span class="params">req, res, next</span>) </span>&#123;</span><br><span class="line">  res.render(<span class="string">'index'</span>, &#123; <span class="attr">title</span>: <span class="string">'Express'</span> &#125;);</span><br><span class="line">&#125;);</span><br><span class="line"></span><br><span class="line">router.get(<span class="string">'/download/:path'</span>, <span class="function"><span class="keyword">function</span>(<span class="params">req, res, next</span>) </span>&#123;</span><br><span class="line">  <span class="comment">// 获取参数</span></span><br><span class="line">  <span class="keyword">let</span> filePath = req.params.path;</span><br><span class="line">  <span class="comment">// 拼接文件的绝对路径</span></span><br><span class="line">  <span class="keyword">let</span> downloadPath = path.resolve(PUBLIC_PATH, filePath);</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 得到文件名</span></span><br><span class="line">  <span class="keyword">let</span> &#123;<span class="attr">base</span>: fileName&#125; = path.parse(downloadPath);</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 文件的信息</span></span><br><span class="line">  <span class="keyword">let</span> stat;</span><br><span class="line">  <span class="keyword">try</span>&#123;</span><br><span class="line">    <span class="comment">// 通过fs模块获取文件的信息，报错就代表着不存在该文件</span></span><br><span class="line">    stat = fs.statSync(downloadPath);</span><br><span class="line">  &#125;<span class="keyword">catch</span>(error) &#123;</span><br><span class="line">    <span class="comment">// 不存在该文件</span></span><br><span class="line">    <span class="keyword">return</span> res.status(<span class="number">404</span>).end();</span><br><span class="line">  &#125;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 获取文件的大小</span></span><br><span class="line">  <span class="keyword">let</span> &#123;<span class="attr">size</span>: total&#125; = stat;</span><br><span class="line">  <span class="comment">// 设置响应头信息，指示内容应该被下载</span></span><br><span class="line">  res.setHeader(<span class="string">"Content-Disposition"</span>, <span class="string">"attachment; filename="</span>+ <span class="built_in">encodeURIComponent</span>(fileName));</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 说明了实体主体内对象的媒体类型，这是一个二进制文件类型</span></span><br><span class="line">  res.setHeader(<span class="string">"Content-Type"</span>, <span class="string">"application/octet-stream"</span>);</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 响应状态为200</span></span><br><span class="line">  res.status(<span class="number">200</span>);</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 通过fs模块创建二进制流，并将其二进制流推送到响应主体中</span></span><br><span class="line">  fs.createReadStream(downloadPath).pipe(res);</span><br><span class="line">&#125;);</span><br><span class="line"></span><br><span class="line"><span class="built_in">module</span>.exports = router;</span><br></pre></td></tr></table></figure>

      
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